1. Field of the Invention
The present invention relates to a method of processing a substrate for removing surface roughness that occurs on a circumferential portion of a substrate to be processed, such as a semiconductor wafer, and films that adhere onto the circumferential portion of the substrate to be processed to become stain sources, and more specifically, the invention relates to a method of processing a substrate for polishing a substrate sidewall surface of a notch portion in a substrate to be processed.
2. Description of the Related Art
In recent years, along with the miniaturization of semiconductor elements and the high packing density of semiconductor devices, management of particles has become more important. As one of the big problems in managing particles, there is the problem of dust occurrence arising from surface roughness that occurs on bevel portions and edge portions of a semiconductor wafer (semiconductor substrate) in processes of manufacturing a semiconductor device. Herein, the bevel portion means a wafer portion having a slanted cross section at an end portion of the semiconductor wafer, and the edge portion means a flat surface wafer portion of around several millimeters from the bevel portion toward the internal side of the wafer.
For example, in a reactive ion etching (RIE) step of forming trenches (deep trenches) of a trench capacitor on a surface of an Si wafer, a by-product generated in etching adheres to the circumferential portion (bevel portions and edge portions) of the wafer. Then, because this by-product works as an etching mask, thorn-shaped protrusions are likely to be formed on the circumferential portion of the wafer (protrusions shown by reference numeral 35 in FIG. 4). In particular, when attempt is made to form an extremely large deep trench whose opening diameter is of a sub micron order, and whose aspect ratio is several tens, the above-mentioned thorn-shaped protrusions are apt to occur at the circumferential portion due to its process conditions.
Although the height of the thorn-shaped protrusions varies with positions on the wafer, it becomes near 10 μm at maximum, and these protrusions are broken at the time of transfer or process of the wafer, and become a cause of particles. Since such particles lead to the decrease of the yield of a semiconductor device being manufactured, it is necessary to remove the thorn-shaped protrusions formed on the circumferential portion of the wafer. Further, in processes of manufacturing a semiconductor device, material films adhering to the circumferential portion of the wafer also become stain sources, and therefore, it is required to remove these material films.
In order to remove such thorn-shaped protrusions and material films, a chemical dry etching (CDE) method and a polishing method are employed. Particularly, in the polishing method, it is advantageous that surface roughness that occurs on the wafer circumferential portion and material films that adhere onto the wafer circumferential portion to become sources of stain can be removed in a short time.
Incidentally, on part of a wafer circumference, as an alignment mark for alignment with a mask, further as a crystal orientation recognition mark for recognizing the crystal orientation on a main surface of the wafer, a cut called “notch” is made in some cases. It is necessary to polish a substrate sidewall surface of the notch portion as well as the circumferential portion.
With regard to polishing of the substrate sidewall surface of the notch portion, a method in which a polishing agent is moved upward and downward in the vertical direction to the wafer surface (horizontal direction) while being contacted and pressed onto the substrate sidewall surface of the notch portion has been most generally used currently. However, in this method, by the contact and pressing to the substrate sidewall surface, further, by the upward and downward movement of the polishing agent to the substrate sidewall surface that is carried out in the vertical direction to the wafer surface, there may be a crystal defect in the wafer. As a result, there may occur a problem in the reliability of a semiconductor device being manufactured. Further, the method has decreased the yield, which has been a problem with the prior art.
On the other hand, there has been disclosed a method in which a polishing head with a shaft in the vertical direction to the wafer surface as its rotational center is applied onto a substrate sidewall surface of a notch portion and the polishing head is rotated to thereby polish the substrate sidewall surface of the notch portion (as disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-234314). Specifically, a grinding stone wheel that has a slot corresponding to the shape of a bevel portion of a wafer is used, and with the slot of the wheel engaged into a circumferential portion of the wafer, the wheel is rotated to thereby polish the substrate sidewall surface of the notch portion. In this method, since the wheel is rotated with a shaft in the vertical direction to the wafer surface as its rotational center, no force in the vertical direction is applied to the wafer, and a crystal defect hardly occurs on the wafer.
However, this method has had the following problem. Namely, because the slot shape of the grinding stone wheel is made to meet the shape of the bevel portion, the general versatility of this method to various kinds of wafers is inevitably low. Further, only the slot portion of the grinding stone wheel is employed as a polishing portion. Therefore, deterioration of the slot inside is large and the durability thereof is insufficient, and when it is deteriorated to some extent, the wheel must be exchanged with a new one, and this will decrease work efficiency, which has been another problem with the prior art.